Electronically controlled fuel injectors typically utilize a solenoid to open and close a small pressure control valve to facilitate injection events. For many years the control valve structure of these electronically controlled fuel injectors utilized a solenoid with an armature attached to move with a valve member. Each injection event involves energizing a solenoid to move the armature/valve member between two stops against the action of a biasing spring. Depending upon whether the valve is two way or three way, one or both of the stops can be valve seats. Soon after the adoption of these electronically controlled fuel injectors, engineers discovered that each fuel injector responded slightly differently to the same control signal. In addition, the response of an individual fuel injector to the same control signal could vary significantly over the life of the fuel injector. These variances from nominal behavior can be attributed to geometric tolerances, slight differences between otherwise identical components, wear, temperature and other factors known in the art as well as other possibly still yet unknown causes.
Engineers soon began devising ways of estimating or measuring how much the behavior of an individual fuel injector deviated from an expected nominal behavior in response to a known control signal, and then applying trimmed control signals so that the individual fuel injector behaved more like a nominal fuel injector. For instance, if a nominal control signal resulted in the fuel injector injecting slightly too much fuel, the trimmed control signal might have a slightly briefer duration than the nominal control signal resulting in the fuel injector injecting about the same amount of fuel as would be expected in response to the nominal control signal. These slight control signal changes are often referred to in the industry as electronic trims.
U.S. Pat. No. 7,469,679 teaches a strategy for trimming electronic control signals to an electronically controlled valve in which the armature and valve member are attached together and move as a unit. In that specific example, a solenoid is energized to move the armature and valve member from contact with a first seat (stop) to contact with a second seat (stop) to open a pressure control passage to either a high pressure source or a low pressure drain to facilitate an injection event. The armature and valve are returned to their original positions when the solenoid is de-energized under the action of a return spring. When the valve member hits a seat, the motion of the armature abruptly stops, causing a brief induced current event in the electronic circuit associated with the solenoid. By comparing the timing of the induced current event to the expected timing of when the valve member should contact the seat, one can measure how much the behavior of that individual electronically controlled valve deviates from nominal, and construct a trimmed control signal that causes the valve member to contact the seat at the expected timing, resulting in a fuel injection event that more closely resembles a nominal fuel injection event.
More recently, electronically controlled valves for fuel injectors have become more sophisticated to the point where, in some instances, the armature can move with respect to the valve member. For instance, one such valve allows the armature to overtravel and decouple from the valve member after the valve member has contacted its seat. Unfortunately, utilizing the trim determination strategy associated with valves in which the armature and valve member move as a unit will not work because the induced current event, if any, does not occur responsive to the valve member contacting its seat. It is valve closure timing, rather than armature motion, that is most important to ascertaining fuel injection variations. While these more sophisticated valves may allow for performance advantages over their previous counterparts, the causes of valve behavior variations remain. Because the old strategies are no longer applicable, developing electronic trim for control signals to these more sophisticated electronically controlled valves can be problematic.
The present disclosure is directed toward one or more of the problems set forth above.